Saturated Vapor Pressure Measurements on Isomeric

J. Chem. Eng. Data

1994,39, 591-594

59 1

Saturated Vapor Pressure Measurements on Isomeric Mononitrotoluenes at Temperatures between 380 and 460 K Karel Aim

E. HBla Laboratory of Thermodynamics, Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, 165 02 Prague 6, Suchdol, Czech Republic

The saturated vapor pressure data of 2-nitrotoluene, 3-nitrotoluene, and 4-nitrotoluene have been measured by comparative ebulliometry over the approximate range 380-460 K with estimated accuracy better than f O . O 1 K in the temperature and better than f0.05% of the measured pressure value. The results obtained were represented by the Antoine equation. No accurate vapor pressures for 2-nitrotoluene and 3-nitrotoluene have been found in the open literature. For 4-nitrotoluene, the present data supplement the vapor pressures reported by Ambrose and Gundry (1980),both sets being in good mutual agreement. The joint vapor pressure data for 4-nitrotoluene were fitted by the Wagner equation, covering the entire range of conditions of the liquid-phase existence.

Introduction

Pure component vapor pressures are the basic data prerequisite to evaluating the vapor-liquid equilibrium in binary and multicomponent systems. When assessing the feasibility of a large-scale separation of the mononitrotoluene isomers by low-pressuredistillation, both the liquid and vapor phases can be considered to a good approximation ideal mixtures, and hence, if dependable, the pure-component vapor pressures represent items of information sufficient for a complete quantitative description of the vapor-liquid equilibrium. However, with the exception of an accurate data set for 4-nitrotoluene covering the temperature range 416-513 K (I),only a few largely discrepant vapor pressure data for the three mononitrotoluenes can be found in the literature (see Tables 5-7 and the references given therein). This paper reports accurate measurements of the vapor pressures of 2-nitrotoluene, 3-nitrotoluene, and 4-nitrotoluene covering the conditions of potential industrial interest, namely, the approximate temperature (and corresponding pressure) ranges of 115-175 O C (3.5-29.5 kPa), 124-179 "C (3.5-25 kPa), and 128-184 "C (3.5-25 kPa), respectively. The uncertainty of the results is estimated better than fO.O1 K in temperature and better than k0.05 % of the pressure. The results were represented by the Antoine equation. The vapor pressures of 4-nitrotoluene were also represented jointly with the data of ref 1by the Wagner equation covering the entire range of liquid existence from the triple point to the critical point. Experimental Section

Materials. All three mononitrotoluene isomers were obtained from VCHZ Synthesia (Pardubice, Czechoslovakia) and purified by procedures recommended in ref 2. The content of impurities was determined by chromatography (Carlo Erba, model GT). The eventual undetectable concentration of impurities (other than water) was always lower than f0.005 mol % . The moisture content was determined by Karl Fischer titration (3). The melting temperature was determined by the microscopic Kofler method, and the freezing point was found according to the standard procedure defined in ref 4. Refractive indices were measured by an Abbe refractometer (Carl Zeiss, Jena). 2-Nitrotoluene. The final middle cut of a two-step batch distillation on a column of 45 theoretical plates at a reflux ratio of 10 was dried over molecular sieves, Fluka (Union Carbide) type 4A, for a week at 20 OC. 0021-9568/94/1739-0591$04.50/0

3-Nitrotoluene. The sample was first treated by steam stripping, and the 15-85 % middle portion of the distillate was redistilled under vacuum. Drying was the same as above. 1Nitrotoluene. The product of an industrial crystallizer was recrystallized three times from absolute ethanol and dried under vacuum a t 40 "C. Afterward the sample was dried and kept in a desiccator above concentrated sulfuric acid. Properties determined for the resulting samples used for vapor pressure measurements are summarized in Table 1. The water used for indirect pressure determinations by means of the water boiling temperatures was a sample redistilled after addition of potassium permanganate in a quartz batch distillation apparatus. Measurements. Saturated vapor pressures were measured by comparative ebulliometry using two very similar ebulliometers, E l and E2, essentially of the standard Swietoslawski design; see, e.g., ref 10. The reference ebulliometer, E l , is filled with water as areference liquid of known vapor pressure and partly enclosed in a perspex box which shields the instrument from temperature fluctuations of the surroundings. The measuring ebulliometer, E2, is filled with the investigated substance and also placed in an insulating box. The experimental arrangement has been previously described (II,12);nevertheless, a brief description is given here. By way of cold (dry ice in acetone) traps, the two ebulliometers are connected in parallel to a pressurecontrolling assembly. The main parts of the assembly are two buffer reservoirs, R1 and R2 (150 dm3 volume each),and an air-thermostated mercury manostat similar to that described by Willingham and co-workers (13). The manostat is furnished with suitably spaced Kovar point contacts which are a part of a control circuit operating a magnetic valve. The valve and simple pneumatic resistors provide connection between reservoir R1 (wherein the pressure is always kept a t a value lower than the measured pressure) and reservoir R2 to which the ebulliometers are connected. When the pressure in reservoir R1 and the pneumatic resistors are appropriately adjusted, the control setup makes it possible to keep the pressure in the ebulliometric system constant within less than 1 3 Pa at a number of approximately fixed pressure values in the range from 1.5 to 100 kPa. The boiling temperatures of a given nitrotoluene sample and of water at a fixed pressure level were measured simultaneously by a quartz thermometer, model HP-2801A (Hewlett-Packard),with two 2850D probes. The thermometer had been calibrated against a Leeds & Northrup standard 0 1994 American Chemical Society

592 Journal of Chemical and Engineering Data,

Vol.39,No.3, 1994

Table 1. Melting Temperatures, Refractive Indices, and Purities of Nitrotoluenes (NT) measd

elit.

ref

content HzO/mol%

chromatog puritp/mol%

1.5461 1.5464

1.5450-1.5466 1.54637-1.5466

5,7 5,7

0.0033 0.0022

>99.995 >99.75c

0.021

>99.995

tioc

compound

measd

2-NT 3-NT

-2.9 15.5 (15.88*) 51.5

4-NT

lit. -4.09 to -2.9 15.52 to 16.1

ref 2,5-7 2, 5-7

51.5 to 52.1

2,6-9

On the basis of the absolute (Le., water-free) sample. * Freezing temperature determined according to ref 4. Containing 0.21 mol % 2-nitrotoluene.

Table 2. Vapor Pressure of 2-Nitrotoluene* TdK TdK PlkPa ATImK APIPa 388.992 388.997 400.395 400.4 18 410.178 410.202 417.988 424.529 424.565 430.154 430.178 435.942 435.990 442.006 442.067 447.894

388.962 388.967 400.363 400.386 410.144 410.168 417.953 424.492 424.528 430.117 430.141 435.904 435.952 441.968 442.029 447.855 mean abs dev (eq 3) standard dev (eq 4)

3.640 3.639 5.773 5.778 8.376 8.375 11.104 13.955 13.946 16.843 16.827 20.322 20.311 24.597 24.587 29.405

5 0 -2 -3 0 -9 -1 15 -2 10 -6

8 -11 8 -12 0 6 8

-1 0 1 1 0 5 1 -15 3 -13 7 -12 18 -17 24 0

7 12

APl% -0.03 0.00 0.01 0.02 0.00 0.06 0.01 -0.11 0.02 -0.08 0.04 -0.06 0.09 -0.07 0.10 0.00 0.04

Table 3. Vapor Pressure of 3-Nitrotoluene* TdK Tw/K PlkPa ATImK APIPa 397.291 397.339 409.044 409.096 419.106 419.174 427.139 427.150 433.899 433.934 439.658 439.660 445.619 445.633 451.824 451.835


3.637 3.638 5.773 5.783 8.375 8.393 11.106 11.107 13.946 13.957 16.828 16.826 20.315 20.325 24.584 24.590

7 -8 1 -1 3 1 3 1 -1 -4 0 -2 -3 -2 3 3 3 4

-2 2 0 1 -2 0 -3 -1 1 4 1 3 4 3 -6

-5 2 3

APl% -0.04 0.05 -0.01 0.01 -0.02 0.00 -0.02 0.00 0.00 0.03 0.00 0.02 0.02 0.02 -0.02 -0.02 0.02

AX = X d c - Xexpt,where X d c have been obtained from eq l b (with parameters given in the last line of Table 5).

AX = X d c - Xexpt,where X d c have been obtained from eq l b (with parameters given in the last line of Table 6).

platinum 25-0 resistance thermometer, 8163-B(provided with an NBS certificate for IPTS-48 and checked periodically for the resistance at 273.16 K by using a water triple point cell and procedure recommended in the monograph (14 ) ) ,coupled in a four-wire connection with the Mueller bridge 8069-B. We believe that, on taking appropriate corrections for the difference between IPTS-48 and IPTS-68according to Riddle et al. (14)and for the difference between IPTS-68 and ITS90 according to McGlashan (15),the measured temperatures were within f0.005 K of the true temperatures on the internationally adopted temperature scales over the range investigated and also well within *0.005 K of the true temperatures over the range of boiling temperatures of water in the reference ebulliometer El. From the boiling temperatures of water the corresponding equilibrium pressures in the system were calculated by using the accurate water vapor pressure equation of Wexler (16). The accuracy in pressure determined in this manner is estimated to be less than *0.05% of the measured pressure value. Typically, a run of vapor pressure measurements on a substance was first conducted in a sequence from the lowest pressure upward and then completed by a series of readings at descending pressures. At the beginning of each run a small portion of the sample (severalmilliliters out of the total charge of approximately 75 mL) was distilled off into the cold trap. This prevented the sample from possible secondary contamination with volatile species on one hand and also made it possible to detect any presence of such impurities by an increase in boiling temperature. For the investigated substances the approximate boiling point elevations observed (per 1-mL sample distilled off) were as follows: 0.008 K/mL for 2-nitrotoluene, 0.005 K/mL for 3-nitrotoluene, and negligible for 4-nitrotoluene.

Table 4. Vapor Pressure of 4-Nitrotoluene. TdK TW/K PIkPA ATImK @/Pa

Results and Discussion For both the temperature 2'68 and 2'90 (as expressed on the IPTS-68 and ITS-90 scales,respectively), the measured vapor

401.311 401.317 413.228 413.282 423.443 423.519 431.605 431.637 438.470 438.521 444.331 444.375 444.386 450.396 450.450 456.848


3.639 3.639 5.776 5.787 8.378 8.400 11.107 11.118 13.946 13.967 16.823 16.845 16.848 20.306 20.332 24.639

3 0 -1 -3 0 0 1

0 2 1 1

0 -1 1 -2 -1 1 2

-1 0 0 1 0 0 -1 0 -2 -1 -1 0 2 -3 3 2 1 2

APl% -0.02 0.00 0.01 0.02 0.00 0.00 -0.01 0.00 -0.02 -0.01

-0.01 0.00 0.01 -0.01 0.01 0.01 0.01

a AX = X d c - Xexpt, where X d c have been obtained from eq l b (with parameters given in the last line of Table 7).

pressures of 2-nitrotoluene, 3-nitrotoluene, and 4-nitrotoluene are presented in Tables 2-4 together with the results of their representation by the Antoine equation. The Antoine equation was employed in the form log(P/kPa) = A - B/[(T,$K) - C] or

where P and T denote the saturated vapor pressure and temperature, respectively, and A , B, and C are adjustable parameters characteristic of a substance and of the temperature scale used.

Journal of Chemical and Engineering Data, Vol. 39, No. 3, 1994 693 Table 5. Comparison of Vapor Pressures and Normal Boiling Point of 2-Nitrotoluene with Literature Data A

constants of eq 1 B

C

approx t range/OC

7.995 90 7.097 75 7.102 10 7.118 37 6.619 44 7.414 10 7.415 60 6.320 43 6.453 42 6.451 39

2898.02 2513.00 2380.18 2448.83 2086.10 2689.06 2677.40 1827.66 1906.532 1904.833

0.0 0.0 26.333 16.546 43.150 0.0 0.0 71.630 65.441 65.587

82-119 50-220 114-220 50-222 129-222 90-223 138-222 129-222 115-175 115-175

~

PlkPa 110 "C

130 O C

150 "C

170 "C

td0C

ref

2.705 3.459 2.701" 2.745 3.047" 2.488 2.678" 2.841" 2.835'

6.4194 7.317 6.103 6.084 6.679 5.546 5.948" 6.419 6.426

14.035' 14.420 12.703 12.466 13.480 11.461 12.254 13.217 13.292

28.596" 26.729 24.645 23.883 25.362 22.184 23.651 25.178 25.457

210.645" 220.366 220.217 222.370 222.151 224.052 221.759 222.068 220.946" 220.906'

20 8 21 22,23 5,24 25 26 27 eq l a eq l b

Extrapolated outside the range of underlying data. Table 6. Comparison of Vapor Pressures and Normal Boiling Point of 3-Nitrotoluene with Literature Data constants of eq 1 approx t PlkPa A B C rangeIoC 110 OC 130 OC 150 "C 170 O C td0C 2618.20 1900.49 1778.69 2579.75 2586.20 2481.45 1993.739 1992.891

7.190 43 6.457 12 6.085 48 7.134 90 7.115 90 7.004 58 6.500 09 6.499 33

0.0 74.311 71.803 0.0 0.0 8.580 61.629 61.697

50-232 171-207 50-207 90-232 140-233 80-232 124-179 124-179

2.276 2.011" 2.358 2.523 2.323" 2.398 1.991"

4.967 4.761" 5.217 5.444 5.023" 5.195 4.595

10.070 10.211" 10.544 10.924 10.095 10.447 9.666

19.155 20.160 19.754 20.583 19.053 19.699 18.807

ref 8 21 22,23 25 26 27 eq la eq l b

231.835 228.102' 234.631" 229.805 232.938 231.833 232.087" 232.041'

Extrapolated outside the range of underlying data. Table 7. Comparison of Vapor Pressures and Normal Boiling Point of 4-Nitrotoluene with Literature Data constants of eq 1 approx t PlkPa A B C range/ O C llO°C 13OOC 15OOC 17OOC td"C 8.359 40 7.106 39 10.336 4 6.191 84 7.149 90 7.406 05 6.648 13 7.074 90 7.172 40 6.272 17 6.367 93 6.365 93

3119.04 2608.90 4528.95 1802.23 2630.00 2889.12 2150.60 2579.75 2640.50 1862.295 1931.718 1930.035

0.0 0.0 -63.019 81.172 0.0 -23.370 43.150 0.0 0.0 75.321 68.661 68.805

92-118 50-238 86-121 114-220

unspecified 54-238 148-233 99-238 138-238 143-226 128-184 128-184

1.655 1.983 1.533 1.674" 1.931" 1.991 2.103" 2.197 1.9094 1.6690 1.681"

4.195" 4.316 4.18W 3.931 4.229" 4.289 4.723" 4.742 4.195" 3.904" 3.916

9.736" 8.729 10.491" 8.353 8.602" 8.625 9.742 9.514 8.556 8.282 8.291

20.944 16.566 24.485 16.331 16.410 16.336 18.691 17.927 16.365 16.190 16.205

217.753" 238.331 207.478" 238.549 238.107" 238.469 233.250 235.758 237.913 238.668" 238.343' 238.302"

ref 20 8 28 21 29 22,23,27 5,24 25 26 1 eq la eq l b

ExtrapcAed outside the range of unL-rlying data. The parameters A, B, and C in eqs l a and l b were evaluated from the experimental vapor pressure data by the method of maximum likelihood, see, e.g., refs 17 and 18, which properly allows for the fact that both the measured variables are subject to certain experimental errors. A symmetric maximum likelihood objective function was used in the form (19) N ~

n=l

where the index n runs over all N experimental observations and UT,,, and up,,, are estimated standard deviations in measured temperature and pressure, respectively, for the nth observation. During calculations on our data these were assigned values UT,,,= 0.01 K and up,,, = 0.0005Pe.,t,, for all n = 1,...,N, as a priori estimated from the properties of the experimental assembly. The parameters of the correlating eq 1 and the calculated values T d c and Pcdccorresponding to each observation were evaluated by minimizing the objective function (defined by eq 2) by an iterative procedure using the simplex method in each of the alternating steps (20). The resulting parameters of eqs l a and l b obtained for the present data on 2-nitrotoluene, 3-nitrotoluene, and 4-nitrotoluene are given in the last two lines of Tables 5-7,

respectively. Tables 2-4 display the corresponding characteristics of the fit for eq lb, namely, the deviations AT = T d c - Texpt and AP = Pcdc- Pexpt, where the values of Tdc and Pcdcare those calculated from eq l b with the resulting parameters at the minimum of the objective function; the deviations in percent of pressure are also included because the second term in the objective function (see eq 2) minimized with the up,,, expressed as a multiple of the nth measured pressure value just corresponds to minimizing the percent deviations in pressure. Also presented in Tables 2-4 are the mean absolute deviations aT and ap given by N

(3) n=l

and the standard deviations ST and sp defined by N

sx = [ ~ ( X c d C- ,X,x,tl,n)2/(N , - M)1-1'2, X = T and P n=l

(4)

where M is the number of parameters in the correlating equation (M = 3 for eq 1). It should be noted that the resulting characteristics of the fit for eq l a are practically the same as those shown in Tables

594 Journal of Chemical and Engineering Data, Vol. 39, No. 3, 1994

2-4 for eq l b and therefore are not displayed; the mean absolute deviations and the standard deviations are identical in all cases, and the single point deviations differ only marginally for a very few data points. Tables 2-4 show that eq 1represents the measured vapor pressure data well within the estimated experimental uncertainties, thus documenting the high precision of the present measurements. The size of deviations increases slightly in the order of substances 2-nitrotoluene, 3-nitrotoluene, and 4-nitrotoluene; this is in accord with the assessment of the purity of the nitrotoluene samples and the boiling point elevations observed a t the onset of the measurements. The comparisons of the present vapor pressures of 2-nitrotoluene, 3-nitrotoluene7and 4-nitrotoluene with the currently available literature data (arranged chronologically)are presented in Tables 5-7, respectively. The tables give the constants of eq 1 (as given in the cited literature sources, recalculated to the units of eq 1,or estimated by K.A. from the results reported in a given original document), the corresponding temperature range of those measurements as well as the vapor pressures a t four temperatures, and the normal boiling temperatures (at 101.325 kPa). Generally, the previous results show large scatter and mutual discordance for each of the substances. Most of the original experimental information dates back to the 1940sor earlier; some of the references contain rounded values, some only equations based on earlier experimental studies, and often there is no mention of the purity. Understandably, most of the values presented in the three comparative tables (except for this work and that of ref 1) are given to more significant digits than appropriate. From Table 5 for 2-nitrotoluene, only the values by Dreisbach et al. (5,24) and the equation presented by Dykyj and Rep66 (27) (based, however, partly on the data by Dreisbach and Shrader (24))are in a relatively good agreement with the present results over the region of overlap. For 3-nitrotoluene (see Table 6), the present results are closest to the results by Hara et al. (26). A distant extrapolation to atmospheric pressure using the Antoine equation based on our results yields the normal boiling point temperature very close to the generally accepted value of 232.6 "C (7). Table 7 documents that, of all literature values, our vapor pressures on 4-nitrotoluene are in very good agreement Gust as expected) with the results of Ambrose and Gundry (1)and that again the extrapolation yields a reasonable normal boiling point (cf. 238.3 "C of ref 7 and 238.675 "C of ref 1; see also comments below). The joint data set of vapor pressures on 4-nitrotoluene composed of the present results and the data of ref 1(excluding the three highest pressure points that Ambrose and Gundry also left out of their fitting procedure) can be correlated by the Wagner equation (30):

where T = 1 - Ta/T,, over the entire liquid range from the triple point (P = 67.27 Pa a t T = 324.79 K; see ref 1)to the critical point (P, = 3207 kPa a t T, = 743 K; see ref l),with the parameters A = -7.709 45, B = 0.611 902, C = -2.756 96, and D = -4.283 78 and with the corresponding characteristics of the fit, given by eqs 3 and 4, as follows: aT = 4 mK, ap = 6 Pa (mean absolute deviation in percent of pressure 0.03), ST = 6 mK, and sp = 9 Pa. These values correspond well with the estimated uncertainties in our measurements and probably also to those in ref 1,even though therein they are not explicitly specified. This can be considered a very good result. Equation 5 with the above constants gives a normal boiling temperature of 4-nitrotoluene tb(1PTS-68)= 238.647 "c;this

corresponds to tb(ITS-90) = 238.607 "C. Since the application of the objective function given by eq 2 (with UT and up taken as above) can be considered more realistic than the (not fully described) method used in ref 1,it is believed that this boiling point may be closer to reality than the value of tb(IPTS-68) = 238.675 K (with an apparently exaggerated accuracy of 3 mK) presented in ref 1. Conclusions

Accurate vapor pressure measurements have been made for 2-nitrotoluene, 3-nitrotoluene, and 4-nitrotoluene over the approximate temperature and pressure ranges 360-480 K and 3.5-30 kPa, respectively. The results have been correlated by the Antoine equation well within the estimated accuracy of the measurements. The present results for 4-nitrotoluene have been successfully correlated jointly with the partially overlapping data set of ref 1by using the Wagner equation covering the entire liquid range. Literature Cited (1) Ambrose, D.; Gundry, H. A. J.Chem. Thermodyn. 1980,12 (6), 559. (2) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of Laboratory Chemicals; Pergamon Press: Oxford, 1966. (3) Mitchell, J.; Smith,D. M. Aquametry;Interscience: NewYork, 1948. (4) Freezing Point Determination; CzechoslovakStandard No. 650311 (orig.: Stanouenl bodu tuhnutl; CSN 650311, in Czech.); Institute for Standardization and Measurement: Prague, 1976. (5) Dreisbach, R. R.; Martin, R. A. Ind. Eng. Chem. 1949,41(12), 2875. (6) Timmermans, J. Physico-Chemical Constants of Pure Organic Compounds; Elsevier: New York, 1950. (7) Weast, R. C., Ed. CRC Handbook of Chemistry and Physics, 62nd ed.; CRC Press: Boca Raton, FL, 1981. (8) Berliner, J. F. T.; May, 0. E. J. Am. Chem. SOC.1926,48, 2630. (9) Lenchitz, C.; Velicky, R. W. J. Chem. Eng. Data 1970, 15, 401. (10) Has, E.; Pick, J.; Fried, V.; V i l h , 0. Vapour-Liquid Equilibrium; Pergamon Press: Oxford, 1967; pp 254-259. (11) Aim, K.; Ciprian, M. J. Chem. Eng. Datu 1980,25, 100. (12) Aim, K.; Svoboda, V.; Majer, V. J. Chem. Thermodyn. 1983,15,531. (13) Willingham, C. B.; Taylor, W. J.; Pignocco, J. M.; Rossini, F. D. J. Res. Natl. Bur. Stand. 1946, 35, 219. (14) Riddle, J. L.; Furukawa, G. T.; Plumb, H. H. Platinum Resistance Thermometry; NBS Monograph 126; NBS: Washington, DC, 1973; 126 pp. (15) McGlashan, M. L. J. Chem. Thermodyn. 1990,22,653. (16) Wexler, A. J. Res. Natl. Bur. Stand. 1976,80A, 775. (17) Rod, V.; HanEil, V. Comput. Chem. Eng. 1980,4, 33. (18) Aim, K. Estimation of Vapor-LiquidEquilibriumParametere.Paper D2.33 presented at the 7th Congress CHISA, Prague, 1981. Also see: Aim, K. Evaluation of parameters inequationsdescribing vaporliquid equilibrium; Inst. Chem. Process Fundam. Rep. No. 62/80, Prague, 1980. (19) Aim, K. Program for the Correlation of Saturated Vapor Pressure Data. Inst. Chem. Process Fundam. Rep. No. 1/81, Prague, 1981. (20) Kahlbaum, G. W. A. 2.Phys. Chem. 1898,26, 577. (21) Levin, E.; Shtern, I. Zh. Prikl. Khim. 1938, 11 (3), 426. (22) Stull, D. R. Znd. Eng. Chem. 1947, 39 (4), 517. (23) Wichterle, I.; Linek, J. Antoine Vapor Pressure Constants ofPure Compounds; Academia: Praha, 1970. (24) Dreisbach, R. R.; Shrader, S.A. Ind. Eng. Chem. 1949,41(12), 2879. (25) Salachijev, V. M.; Sharnin, G. P. Tr. Kazun. Khim.-Tekhnol. Inst. 1973, 52, 69. (26) Hara, Y.; Osada, H. J.Ind. Explos. Soc., Jpn. (KogyoKagaku) 1976, 37 (5), 233. (27) Dykyj, J.; RepP, M. Vapour Pressures of Organic Compounds

(orig.: Tlak nns9tenej pary organick9ch zlLEenln; in Slovak); Veda: Bratislava, 1979. (28) Mann, C. A.; Montonna, R. E.; Larian, M. G. Ind. Eng. Chem. 1936, 28 (5), 598. (29) Kobe, K. A.; Okabe, T. S.; Ramstad, M. T.; Huemmer, P. M. J.Am. Chem. SOC.1941,63,3251. (30) Wagner, W. Cryogenics 1973,8, 470.

Received for review December 15, 1993. Accepted April 20, 1994.. The present study was partially supported by the Grant Agency of the Academy of Sciences of the Czech Republic (Grant No. 472413) and by the Grant Agency of the Czech Republic (Grant No. 203/93/ 2287). e

Abstract published in Advance ACS Abstracts, June 1, 1994.

Saturated Vapor Pressure Measurements on Isomeric

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